4-pole electromagnetic inductiontype protective relay having improved coil connections



Jan. 2, 1968 P. KOTOS 3,361,935

4-POLE ELECTROMAGNETIC INDUCTION-TYPE PROTECTIVE RELAY HAVING IMPROVED COIL CONNECTIONS Filed Oct. 4, 1965 jx Fig.2

XF I 9 I /NVEN7'0R PETER Koros,

AT TORNE Y United States Patent 3,361,935 4-POLE ELECTROMAGNETIC INDUCTION- TYPE PROTECTIVE RELAY HAVING IM- PROVED COIL CONNECTIONS Peter Kotos, Drexel Hill, Pa., assignor to General Electric Company, a corporation of New York Filed Oct. 4, 1965, Ser. No. 492,484 4 Claims. (Cl. 317-36) This invention relates to electromagnetic induction relays, and more particularly it relates to improved coil connections in a 4-pole distance relay having a reactance operating characteristic.

Distance relays are used in the art of protective relaying to perform rapid and accurate circuit controlling functions in response to predetermined phase and magnitude relationships between alternating currents and voltages derived from a protected electric power transmission line. Such a relay is said to have an angle-impedance or ohm operating characteristic when its operation is controlled by the resultant of two quantities dependent, respectively, on the square of transmission line current and the phasor product of line current and volt age. The relay picks up whenever the ratio of line voltage to line current, which is the apparent impedance of the protected line, becomes less than a predetermined constant magnitude at a given critical angle. The critical angle is fixed by design; when made equal to 90 degrees the relay will respond at constant reactance and thereby ignore'whatever arc resistance is associated with any transmission line fault within its reach.

The general principles and usual applications of reactance relays are well known in the art. (See for example the paper written by A. R. VanC. Warrington, Application of the Ohm and Mho Principles to Protective Relays, 65 Transactions of the American Institute of Electrical Engineers 378 [June 1946].) The relay can advantageously be constructed according to the teachings of US. Patent 2,131,605 granted to O. C. Traver on Sept. 27, 1938. However, such a relay will tend to overreach or underreach under relatively low current, high power factor fault conditions. It may erroneously operate at a higher level of fault reactance than desired, or it may fail to operate at the desired constant reactance level. .Thus in practice the theoretically flat or straight-line op erating characteristic of the relay will not be obtained over the full range of possible fault conditions.

Accordingly, it is a general object of my invention to provide an improved induction-type protective relay characterized by greater security and reliability than has heretofore been obtained.

Another object is to provide improved coil connections in such a relay for the purpose of reducing overreach without adversely affecting the burden of the relay or its manufacturing cost.

' In carrying out my invention in one form, I provide an electromagnetic relay comprising a frame or stator that includes a continuous magnetic path effectively separated into four sections by four salient poles projecting symmetrically therefrom. A magnetizable core is spaced apart from the pole faces to define therewith four essentially identical gaps, and a circuit controlling, current conducting armature is disposed for movement through these gaps. On the stator I provide a plurality of magnetic flux producing coils that are adapted to be energized by at least two different A-C electric quantities. (To obtain a reactance operating characteristic, for example, one of these quantities is proportional to transmission line current I and another is dependent on IZ E, where E is line voltage and Z is a design constant.) As a result of the interactions of the magnetic fields established in the aforesaid gaps by the energized coils, driving torque is established in the armature, and with the various coils appropriately arranged for a reactance relay, this driving torque will comprise an operating component proportional to I Z and a restraining component proportional to the product of IE and the sine of the phase angle between I and E.

According to my invention, the relay coils that are adapted to be energized by the line current derived quantity are located on non-adjacent poles of the stator, while the coils adapted to be energized by the other quantity (derived from IZ E) are respectively located on the four sections of the aforesaid magnetic path. By interconnecting the latter coils so that those on alternative sections of the path are in series with each other and the two series combinations thus formed are in parallel, I have been able to maintain the operating characteristic of the relay substantially flat for relatively high are resistance line fault conditions and over the full practical range of fault current magnitude without unduly increasing the relay burden.

My invention will be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a schematic diagram of a preferred embodiment of my invention; and

FIG. 2 is a graphical representation of the operating characteristic of this relay, in terms of impedance.

Referring now to FIG. 1, the illustrated embodiment of my invention is seen to comprise a frame structure or stator 10 constructed of laminated magnetizable material and having four symmetricalyy disposed salient poles 11, 12, 13 and 14. The body of stator 10 forms a closed magnetic path or loop which is effectively divided into four consecutive parts or sections 15, 16, 17, and 18 by the four salient poles. Preferably the poles project from the stator body toward a centrally located axis 19 and terminate in inwardly disposed concave pole faces.

A magnetizable member or core 20 is located inter mediate the salient poles 11-14 and is spaced apart from their extremities to define therewith four gaps which are symmetrically located with respect to the axis 19. The core 20, which preferably is a cylindrically shaped member physically annexed to the stator, provides a common link in the complete magnetic circuit for magnetic flux issuing from the extremities of the respective poles.

An electroconductive armature or rotor 21 is mounted pivotally on axis 19 for rotation through the gaps formed by the core 20 and the faces of the four stator poles 1114. A portion of the surface of this current conducting induction element 21, which preferably is a lightweight, cup-shaped member fitting loosely on the cylindrical core 20, extends into these gaps for movement in a direction generally parallel to the pole faces, and thus the current conducting path provided by the rotor lies substantially transverse to the magnetic fields between the core and the respective pole faces. The rotor 21 is actuatable in either direction by driving torque created by the interaction of the magnetic fields in the rotor. Rotation of the rotor in a clockwise direction can be made to open or close a suitable switch contact, not shown, for the performance of a circuit controlling operation.

The mechanical structure of the relatively compact stator and rotor described thus far is well known in the art. If desired, the improvements that are the subject matter of my co-pending patent application can be used. It should be clearly understood, however, that the present invention is not limited by the use of this particular relay construction.

As can be seen in FIG. 1, various electrical coils or windings are disposed on the stator 10. Four of the coils 22-25 having equal turns are located in pairs on the non-adjacent stator poles 11 and 13, respectively. Another four coils 26-29 having equal turns are respectively located on the four parts 15-18 of the stator body.

In the illustrated embodiment of my invention, the coils 22 and 24, mounted on the diametrically opposed poles 11 and 13, respectively, are serially connected to a first pair of input terminals 30a and 30b. The associated coils 23 and 25 are similarly connected in series circuit relation to another pair of input terminals 31a and 31b. The first and third coils 26- and 28 of the group of coils on the body of the stator 10 are connected in series between a third pair of input terminals 32a and 32b, and in accordance with my invention the second and fourth coils 2'7 and 29 of this group are connected between the same terminals 32a and 32b in series with each other but in parallel with their complementary coils 26 and 28. All of the coils 22-29 when energized by alternating electric quantities supplied to the input terminals produce in stator 10 magnetic fluxes proportional to the quantities supplied.

In order to obtain the operating characteristic of a reactance relay, the input terminals 30a and 30b of the relay are connected to the secondary winding of a current transformer 33 associated with a primary conductor L1, and the input terminals 31a and 31b are connected to another current transformer 34 associated with a parallel conductor L2. The conductors L1 and L2 represent two lines of a 3-phase, 3-wire alternating electric power transmission system. The current transformers 33 and 34 derive alternating currents proportional to the currents in the protected lines and supply these quantities to the two pairs of terminals 30a, 30b, and 31a, 31b for energizing the coils 22, 24 and 23, 25, respectively. On the other hand, the input terminals 32a and 32b of the relay are connected by means of a parallel R-C circuit 35, 36, a secondary winding 37c of a transactor 37, and a voltage divider 38 to a pair of potential transformers 39 and 40. The potential transfonmers 39 and 40 are coupled to transmission line conductors L1 and L2 as shown, whereby the voltage taken across the voltage divider 38 is proportional to the primary or phase voltage E between these conductors. I

The transactor 37 is a well known device having electrical characteristics similar in some respects to a conventional transformer and similar in other respects to a reactor. It comprises in effect an air-gap reactor having associated therewith two primary windings 37aand 37b and a secondary winding 370. A potentiometer 41 is shown connected across the secondary winding 37c. The voltage developed across the tapped portion of the potentiometer 41 is therefore representative, both in magnitude and phase, of the net A-C current flowing in the primary windings 37a and 37b. This voltage is related to net primary current by a complex proportionality constant or vector operator Z known as the transfer impedance of the transactor. The transactor primary winding 37a is included in the secondary circuit of the current transformer 33, and the companion primary winding 37b is connected with opposite polarity in the secondary circuit of current transformer 34, whereby the net primary current is proportional to the difference or phase current I being conducted by the protected transmission lines L1, L2. Consequently, the voltage obtained from potentiometer 41 is proportional to IZ and the relay input terminals 32a and 32b are energized in accordance with the quantity lZ -E.

As is shown in FIG. 1, the two relay coils 26 and 28 are arranged in a manner to produce, when energized by the alternating electric quantity supplied to the terminals 32a and 32b, opposing magnetic fluxes in the closed magnetic path of the stator 19. That is, when energizing current is flowing in the circuit of these serially interconnected coils in a given instantaneous direction, such as from input terminal 32a to input terminal 32b, the magnetic flux produced by the coil 28 in part 17 of the stator will be in a direction (clockwise as viewed in FIG. 1 for the specified current direction) opposite to the direction of flux produced in part 15 by the companion coil 26 (counterclockwise). Similarly, the serially interconnected coils 27 and 29 are so arranged that, when energized by the same quantity, coil 27 will produce magnetic flux in a direction aiding that of coil 26 but opposing that of coil 28, while coil 29 will produce magnetic flux in a direction aiding that of coil 28 but opposing that of coil 26. It will therefore be apparent that the four coils 26-29 on the stator body produce in the side poles 12 and 14 magnetic flux proportional to the quantity energizing the pair of input terminals 32a and 32b.

The serially interconnected coils 22 and 24, which are located, respectively, on the top pole 11 disposed at the intersection of stator parts 15 and 16 and on the bottom pole 13'disposed at the intersection of stator parts 17 and 18, are arranged in a manner to produce, when energized by alternating current in the secondary circuit of the current transformer 33, mutually aiding magnetic fluxes. The associated coils 23- and 25, also located respectively on the poles 11 and 13, are arranged to produce, when energized by current in the secondary circuit of the current transformer 34, magnetic fluxes opposing those of the coils 22 and 24. Consequently the net magnetic flux in the poles 11 and 13 is proportional to the difference or phase current I in the transmission line conductors L1, L2.

By locating the current-energized c-oils 22-25 on the poles 11 and 13, I have been able to utilize the body of the stator 10 as a shield to avoid or at least to minimize undesirable magnetic affects on external devices, such as other electromagnetic relays located nearby, by stray fields associated with these coils.

The fluxes produced upon energization of the various coils 22-29 establish magnetic fields in the four gaps for-med between the pole faces of the stator 10 and the core 20. In a manner well known to those skilled in the art, the magnetic fields interact in the rotor 21 to create a driving torque for actuating the rotor. The net torque acting on the rotor 21 is the sum of the torque components contributed by the interaction of the magnetic fields in adjacent pairs of gap, which components are respectively proportional to the product of the ampere-turns of the coils producing the involved fields. Thus for the illustrated reactance relay, this torque can be represented by the expression: K1 (IZ -E) sin B, where K is a design constant and B is the angle between I and (IZ -E).

It is assumed that positive or clockwise movement of the rotor 21 is required for relay operation. Whenever the resultant or net driving torque is positive, the relay 0perates to perform its preselected control function, and whenever the net driving torque is negative, no operation is obtained. The condition of zero torque, therefore, defines the operating limits of the relay. Thus by equating the foregoing torque expression to zero, dividing through by 1 and rearranging, the following equation describing the operating characteristics of the relay shown in FIG. 1 is derived: Z sin 0=X where Z is the apparent impedance of the transmission line as seen by the relay (i.e., the ratio of transmission line voltage E to transmission line current I as reflected by the potential and current transformers), 0 is the phase angle between the E and I (i.e., the power factor angle), and X is a predetermined constant equal to Z sin 5 being the angle by which IZ leads I). Whenever the reactance of the transmission line becomes less than X the net driving torque of the rotor 21 is positive and relay operation is then obtained.

This operating characteristic can be conveniently illustrated on the conventional R-X impedance diagram shown in FIG. 2. The origin in this diagram represents the point in the electric power system where the current and potential transformers supplying line-voltage and line-current derived quantities to the'relay are coupled thereto, while the abcissa R and ordinate jX describe values of resistance and inductive reactance respectively, as determined by the phasor relationship between line voltage and current measured by these transformers. The straight line X parallel to the R axis represents the loci of apparent impedance values which define the operating range of the illustrated relay. Any phase fault on the protected line of such a nature that the impedance to the fault falls below the line X will be within the operating range (ohmic reach) of the relay.

The vector Z in FIG. 2 represents a typical value of fault impedance having a reactance component just equal to the X and a resistance component R This impedance is equal to the ratio of voltage E to fault current I in the faulted line. It will be observed that the magnitude of I at the operating point of the relay depends on the relative magnitude of R which in turn depends on the amount of arcing resistance at the fault location. Consequently, less current is required for relay operation under conditions of high arcing resistance than under conditions of low arcing resistance. This means that at the operating point the magnitude of the IZ -E quantity that energizes the relay input terminals 32a and 32b can vary from nearly zero if arcing resistance were negligible to relatively high levels if arcing resistance were substantial.

To preserve the desired straight-line operating characteristic of the relay over the full magnitude range of the input quantity supplied to its terminals 32a and 32b, it is important to maintain a relatively constant, undistorted relationship between this quantity and the resulting magnetic fields established in the gaps defined by the extremities of the side poles 12 and 14 of the stator 10. I have found that in relays of practical design and cost there are small variations in the dimension of the stator laminations, and sometimes in the number of turns of the respective coils 2.649. As a result, flux density tends to be unequal in the respective parts 1518 of the stator when identical current is flowing through the interconnected coils 26-29, and at high magnitudes of the input quantity one quarter of the stator may begin saturating before the remainder. This causes the relay to overreach or underreach, and the relay operating characteristic deviates from the desired straight line. However, by connecting the coils 2649 in the manner shown in FIG. 1 and previously described, I have been able to obtain a more equal flux distribution in the stator without unduly increasing the volt-ampere burden of these coils.

While I have shown and described a preferred form of my invention by way of illustration, various modifications and refinements will occur to those skilled in the art. It should be understood that the usefulness of my invention is not limited to the particular external circuit connections to the relay input terminals that have been shown for purposes of illustration. I contemplate therefore by the claims which conclude this specification to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electromagnetic induction relay responsive to predetermined relationships between two electric quantities derived from an electric power system:

(a) a magnetizable stator providing a closed magnetic path and having four poles effectively separating said path into first, second, third, and fourth consecutive parts;

(b) a magnetizable member spaced apart from the extremities of said poles to define therewith four p (c) a circuit controlling current conducting memb disposed for movement through said gaps;

(d) first, second, third, and fourth coils located respectively on said first, second, third, and fourth parts of said magnetic path,

(i) said first coil being connected in series with said third coil for energization by one of the two electric quantities, and said second and fourth coils being connected in series with each other but in parallel with said first and third coils for energization by the same quantity,

(ii) said first and third coils being arranged to produce, when energized, opposing magnetic fluxes in said first and third parts of said path, said second coil being arranged to produce, when energized, magnetic flux in said second part opposing the magnetic flux that said third coil produces in said third part, and said fourth coil being arranged to produce, when energized, magnetic flux in said fourth part opposing the magnetic flux that said first coil produces in said first part; and

(e) at least one other magnetic flux producing coil located on the two poles of the stator that are disposed, respectively, at the intersection of said first and second parts and at the intersection of said third and fourth parts of said path, said other coil being connected for energization by the other of the two electric quantities.

2. The relay of claim 1 in which said other quantity is derived from system current.

3. The relay of claim 2 in which said one quantity is proportional to the difference between system voltage and the product of system current and a predetermined impedance.

4. An electromagnetic relay comprising:

(a) first and second pairs of input terminals adapted to be energized by alternating electric quantities;

(b) a magnetizable core having an axis;

(c) a magnetizable stator having a body providing a closed magnetic path and first, second, third, and fourth poles projecting symmetrically from said body, said first and second poles defining a first section of said magnetic path, said second and third poles defining a second section of said path, said third and fourth poles defining a third section of said path, and said fourth and first poles defining a fourth section of said path with the faces of the respective poles being spaced from said core to form four gaps;

(d) a circuit controlling electroconductive armature supported for rotation about the axis of said core and having a portion disposed in said gaps in overlapping relation with said pole faces;

(e) a plurality of magnetic flux producing coils located respectively on said first, second, third, and fourth parts of said magnetic path, the coils on said first and third parts being serially connected between said first pair of input terminals and the coils on said second and fourth parts being serially connected between the same terminals in parallel with the coils on said first and third parts, said coils being arranged to produce in said first and third poles magnetic flux proportional to the electric quantity energizing said first pair of input terminals; and

(f) means for producing in said second and fourth poles magnetic flux proportional to the electric quantity energizing said second pair of input terminals.

References Cited UNITED STATES PATENTS 5/1935 Van C. Warrington 317-36 MILTON O. HIRSHFIELD, Primary Examiner. J. D. TRAMMELL, Assistant Examiner. 

1. IN AN ELECTROMAGNETIC INDUCTION RELAY RESPONSIVE TO PREDETERMINED RELATIONSHIPS BETWEEN TWO ELECTRIC QUANTITIES DERIVED FROM AN ELECTRIC POWER SYSTEM: (A) A MAGNETIZABLE STATOR PROVIDING A CLOSED MAGNETIC PATH AND HAVING FOUR POLES EFFECTIVELY SEPARATING SAID PATH INTO FIRST, SECOND, THIRD, FOURTH CONSECUTIVE PARTS; (B) A MAGNETIZABLE MEMBER SPACED APART FROM THE EXTREMITIES OF SAID POLES TO DEFINE THEREWITH FOUR GAPS; (C) A CIRCUIT CONTROLLING CURRENT CONDUCTING MEMBER DISPOSED FOR MOVEMENT THROUGH SAID GAPS; (D) FIRST, SECOND, THIRD, AND FOURTH COILS LOCATED RESPECTIVELY ON SAID FIRST, SECOND, THIRD, AND FOURTH PARTS OF SAID MAGNETIC PATH, (I) SAID FIRST COIL BEING CONNECTED IN SERIES WITH SAID THIRD COIL FOR ENERGIZATION BY ONE OF THE TWO ELECTRIC QUANTITIES, AND SAID SECOND AND FOURTH COILS BEING CONNECTED IN SERIES WITH EACH OTHER BUT IN PARALLEL WITH SAID FIRST AND THIRD COILS FOR ENERGIZATION BY THE SAME QUANTITY, (II) SAID FRIST AND THIRD COILS BEING ARRANGED TO PRODUCE, WHEN ENERGIZED, OPPOSING MAGNETIC FLUXES IN SAID FIRST AND THIRD PARTS OF SAID PATH, SAID SECOND COIL BEING ARRANGED TO PRODUCE, WHEN ENERGIZED, MAGNETIC FLUX IN SAID SECOND PART OPPOSING THE MAGNETIC FLUX THAT SAID THIRD COIL PRODUCES IN SAID THIRD PART, AND SAID FOURTH COIL BEING ARRANGED TO PRODUCE, WHEN ENERGIZED, MAGNETIC FLUX IN SAID FOURTH PART OPPOSING THE MAGNETIC FLUX THAT SAID FIRST COIL PRODUCES IN SAID FIRST PART; AND (E) AT LEAST ONE OTHER MAGNETIC FLUX PRODUCING COIL LOCATED ON THE TWO POLES OF THE STATOR THAT ARE DISPOSED, RESPECTIVELY, AT THE INTERSECTION OF SAID FIRST AND SECOND PARTS AND AT THE INTERSECTION OF SAID THIRD AND FOURTH PARTS OF SAID PATH, SAID OTHER COIL BEING CONNECTED FOR ENERGIZATION BY THE OTHER OF THE TWO ELECTRIC QUANTITIES. 